Magneto



Feb. 18, 1941.

K. A. HARMON MAGNETO Filed June 27, 1939 2 Sheets-Sheet 1 ILL/III 11, 111 I 111' I II 0 M 7 .2 M 7 m r J m 7m w m N H m m 7 %2 g "J w 3 ATTORNEYS Patented Feb. 18, 1941 UNITED STATES PATENT OFFICE MAGNETO Application June 27, 1939, Serial No. 281,385

3 Claims.

This, invention relates to an improved magneto designed for use in signalling systems, such for example as certain telephone systems.

Heretofore, the magnetos used for such systems have been of the wound-armature type which entails the use of slip rings and brushes to conduct the current from the rotating generating coil. These rings and brushes are a source of frequent trouble and it is desired to eliminate them and resort to a type of magneto wherein the generating coil is stationary, and the rotor carries the magnets. This type, however, makes necessary a rotor of larger diameter and this, in turn, necessitates many changes in the construction, mounting, and arrangement of parts.

This invention has for an object to provide a magneto of unwound-rotor type which will be at least no larger than the wound-armature type of magneto and will at least fit withinthe same space occupied by the wound-armature type of magneto, characterized by provision of a novel form of crank-operated hand drive for the rotor; a novel form of switch actuating means; and other features relating to the construction,

' mounting and arrangement of parts.

These features will best be understood as the detailed description proceeds.

The invention will be disclosed with reference to the accompanying drawings, in which:

Fig. 1 is a sectional elevational view of a magneto involving the invention;

Fig. 2 is a cross sectional view thereof taken on the line 2-2 of Fig. 1;

Fig. 3 is a fragmentary ,view of a part of the operating handle, looking in a direction at right angles to that in which Fig. l was taken;

Fig. 4 is a cross sectional view taken on the line 44 of Fig. 1 showing the switch mechanism;

Fig. 5 is a sectional plan view taken on the line 5-5 of Fi 4;

Figs. 6 and 7 are side and front elevational views, respectively, of the cam mechanism for actuating the switch mechanism; and

Fig. 8 is a dia'grammatical view showing the electrical connections of the apparatus.

Referring to these drawings: the magneto includes an open-topped hollow box-like housing member i0 (Figs. 1 and 2) of molded non-magnetic material which may, for example, be of some suitable plastic material. In the rear 'wall of this member is fixed a tubular stud H which extends horizontally into the interior of the hollow member ll]. Also fixed in the same wall is a stud l2 which extends outwardly therefrom at a level above stud I l. Both studs may be inset into the member l3 during the casting process or fixed thereto in any other suitable way. The front wall of member ID has an outward tubular extension I3 of approximately square cross section, forming a compartment I4. Connecting this cpmparement H with the interior of the member i0 is an opening l5 of modified cylindrical form. Shoulders l6 are formed at the intersection of the compartment ll with opening l5 and seated against these shoulders is a panel I! of insulating material, fixed to the housing by cap screws i8. The panel has fixed thereto a bushing I9 located coaxially with stud H for a purpose to be described. The panel i1 closes the opening I5 except for a narrow slot 20, formed between its upper edge and the top wall of extension I3. A cover 2|, held in place by a pin 22 fixed in one side wall of extension I3 and by a screw 23 in the opposite side wall of said extension, closes the outer end of compartment H. The upper, end of member I0 is closed by a cover 25, held in place by cap screws 26, threaded into the upper wall of member ID.

The magneto includes a stator made up of three laminated-iron members (Fig. 2) including two side members 21 and a bridging member 28, mounted in the form of an inverted U. A coil 29 is mounted on the bridging member 28 or core. The side members are secured to member III by being inset therein during the molding process or in any other suitable way. Each side member consists of a stack of laminations bound initially together by rivets 30 and set into the non-magnetic side walls of member In. The core 28 is also made up of a stack of laminations, bound together by rivets 3|. The ends of the core test one on top of each side member 21 and are held in place by clips 32 and cap screws 33, threaded into the upper ends of members 21. The confronting lower parts of the side members 21 are of concave formation, finished in t ue coaxial relation with stud H.

The rotor includes two short but powerful magnets 35 and pole shoes 36 therefor. The shoes 36 are made up of iron laminations, initially bound together by rivets 31. The magnets and shoes are assembled, as shown, with like poles of the magnets interconnected by the shoes, and these parts are then placed in a mold and the latter filled with non-magnetic material 38 which binds the parts together. This part 38 dovetails into each pole shoe and shrinkage of the cast material draws the shoes tightly against the ends of the magnets 35. The material 38 also tatably mounted on the exterior of stud |l. Into the other end of this same bore fits a hub 4| which has a flange 42, fixed by screws 43 to one end face of the rotor. The rotor is held against axially-endwise movement in either direction by the engagement of the bushing 46 with the rear wall of member l0 and by the engagement of flange 42 with the inner end face of bushing |9.

The rotor has a drive shaft which is rotatably supported near one end in a bearing bushing 46, fixed in the outer end of the tubular stud II. The shaft projects beyond the outer end of stud H to receive a pinion 41, fixed thereon. The shaft also extends inwardly beyond its bearing 45, through the hollow stud through the hub 4| and bushing l9, terminating with a button 48 of insulating material, located in the compartment l4. The shaft 45 is mounted to slide in an axial direction in the bearing 46, the hub 4| and bushing l9 and ,it is free to turn in the bearing and bushing. A pin 49, fixed in and passing diametrically through shaft 45, has radially projecting ends which are engaged in slots 50 formed in hub 4|, thereby providing a driving connection between the shaft and rotor. Provision is made for a limited amount of relative turning movement between the shaft and hub 4| For example, each slot 59 is made as a portion of a helix, as best shown in Fig. 6. The slots therefore act as cams whereby, if the rotor is held against rotation and shaft 45 is turned in the proper direction, the cam slots 59 acting on pin 49 cause the shaft tov move axially to theleft until the ends of the pin strike the bottoms of the slots. Thereafter the pin ends will drive the rotor and will remain in the bottoms of slots 56 until the turning effort on shaft 45 is stopped. Then the shaft will move axially to the right under the influence of a spring 52, which is coiled around shaft 45 and acts between a washer 53 (abutting pin 49) and a collar 54 fixed to shaft 45. The engagement of collar 54 with the inner end of bearing 46 limits the outward movement (to the right) of shaft 45. The rotor itself is held against any appreciable axial movement.

The rotor also tends to remain in the position shown in Fig. 2 by reason of the powerful pull of the magnets 35 on the stator element. when shaft 45 is first turned, the rotor remains stationary until the ends of pin 49 have advanced in the cam slots 56 and reached the bottoms thereof, whereupon continued turning of the shaft drives the rotor in unison therewith.

This axial movement of shaft 45 is utilized to actuate a switch which serves to open the talking circuit of a telephone and close a ringing circuit. This switch is, or may be, of the'usual and wellknown formand the functions it performs in telephone circuits and such circuits themselves are, or may be, of the usual and well-known form. As shown herein, the switch is mounted in the compartment I4 (Figs. 4 and 5) and includes a spring switch arm 56 having on opposite sides thereof near its outerand free end, a pair of contacts 51 and 56. This switch arm plays between two fixed conducting strips 59 and 66, bearing contacts 6| and 62 respectively. The spring in Thus,

panel l1, to a terminal screw 64. Strip 59, 1ikewise suitably fixed to panel i1, is connected to the terminal screw 29, above described. Strip 66 is fixed, as indicated, to panel l1 and connected thereto by one of the described screws I8 is one terminal wire 65 of coil 29. The other terminal wire 66 of coil 29 is connected by another of the screws l6 to a conducting strip 61, also fixed to panel l1, and having connected thereto a termi nal screw 66. The wires 65 and 66 extend through the slot 29, above described.

The conventional talking circuit of the telephone is connected to terminal screws 23 and 64,

whereby such circuit is controlled by switch 56, being closed when the magneto is not in operation. When signalling is to be eifected, the magneto is operated, whereupon the talking circuit is opened by switch 56 and a ringing or signalling circuit closed thereby, whereby the magneto coil 29 is connected acrossthe terminal screws 64 and 66, the latter being grounded as indicated. Thus, a bell-ringing, alternating-current generated by the magneto, may be transmitted over a circuit which includes a wire connected to terminal screw 64 as one side of the circuit and the ground as the other side of the circuit.

The case of the telephone is shown in part by dotted lines at 69 in Figs. 1 and 4.

For operating the magneto, the usual handoperated crank is provided. A crank 16 is screw threaded onto the hub of a gear 1| which is rotatably mounted on the stud l2 and meshes with the pinion 41. The gear 1| is held in axial position between a shoulder 12 on the stud and the head of a cap screw 16 threaded into the stud. The crank 16 has a folding handle 14 which is normally held in the position illustrated in Fig. 1 by a spring 15. The handle has a stud 16 which is rotatably mounted in two spaced ears 11 formed on the handle. The spring is coiled around this stud and the ends of the spring are connected one to the crank 16 and one to the stud 16. A pin 16 fixed to stud 16 is adapted by abutment with the left hand side of crank 16 to limit the outward or clockwise movement of the handle. When-the handle 14 is released, the spring 15 restores it to the position illustrated in Fig. 1 wherein it is entirely housed-in a cylindrical recess 66 in the casing 69.

In operation, rotation of the magnetic rotor is resisted by the magnetic pull which is exerted on the laminated stator. .Hence, when the operator turns the crank 16 to drive shaft 45, the r0- tor does not immediately turn. Rather, in its initial stage of rotation, shaft 45 turns without turning the rotor and this portion of the rotation of the shaft is utilized, through the pin 49 and helical slots 56, to cause an axial movement of the shaft to the left, as viewed in Fig. 1. The rotor, as above described, is held against any substantial axial movement. The switch 56 is thus actuated to open the talking circuit of the telephone apparatus by separating the contacts 51 and 6| and to close the ringing or signalling circuit by engaging the contacts 56 and 62. The

shaft, having thus moved the switch, also maintains it in the described position as long as driving torque is applied to shaft 45, After the switch has been thus actuated, the pin 49 enages the inner and closed end of each slot BI and thereafter the rotor is positively driven from the shaft. When the driving torque on shaft is relaxed, the rotor comes to rest in the illustrated position and the spring 52 moves the shaft to the right into the illustrated position, thus moving the switch 58 back into the illustrated position and closing the talking circuit.

The invention affords a magneto which is somewhat smaller in height and length than the conventional wound-armature type of magneto and which is much more powerful due to the use of the magnets 35 which, although small, are of exceedingly high coercive force. The difiiculties, resulting from the use of slip rings and brushes, are overcome by making the coil stationary. The use of a stationary coil and the shortest possible magnetic circuits, makes necessary the elimination of the conventional type of crank shaft and the substitution of a crank-operated gear mounted on a stud outside the housing Ill. The circuit closer 56 has to be actuated from the rotor shaft and this is effected in the novel manner above described, One end of the chamber in which the rotor is mounted has been partitioned oil by the panel I! to form a compartment ll in which the circuit closer and its contacts are housed and protected against dust and dirt as well as mechanical injury.

What I claim is:

1. In a signalling magneto, a laminated stator element, a coil thereon, a magnetic rotor cooperating with said element to establish a magnetic circuit therethrough and vary the flux in such circuit, a frame supporting said element, a hollow stud fixed to said frame and on which said rotor is mounted, means for holding said rotor 2. In a signalling magneto, a laminated stator element, a coil thereon, a magnetic rotor coopcrating with said element to establish a magnetic circuit therethrough and vary the flux in such circuit, a frame supporting said element,'a hollow stud fixed to said frame and on the exterior of which said rotor is mounted, means for holding said rotor against any substantial movement axially of said stud, a hearing within said stud near the outer end thereof, a drive shaft rotatably mounted in said bearing and extending entirely through'and beyond the inner end of said stud, a hub fixed to the rotor and loosely mounted on said shaft with an end face located adjacent the inner end of said stud, said hub having a helical slot extending from said end face inwardly a short distance, a pin fixed to said shaft and hav ing a part engaged in said slot, resilient means tending to hold the shaft in an axial position wherein the .pin lies in the entrance end of said slot, and means for rotating said shaft, whereby since rotation of the rotor is resisted by the magnetic pull on the stator, the shaft initially turns without turning the rotor until said pin engages the inner end of said slot and whereby the shaft moves axially against the force of said resilient means into a second axial position, and a switch in circuit with said coil and actuated by movement of said shaft into said second axial position.

3. In a signalling magneto, stationary and movable elements effective on relative movement to produce a change of magnetic flux and cause the generation of an electromotive force, a shaft for driving" said movable element, a housing for supporting and enclosing both said elements and including one upstanding wall in which said shaft is supported and an opposed upstanding wall having an opening therethrough leading to one end face of the movable element, a panel fixed in said opening and having an inner face located adjacent said end face of the movable element and partitioning said opening, a switch mounted on the outer face of said panel, a cover closing the outer end of said opening, and means for moving said shaft axially on initial rotation of said movable element, said shaft having a part extending through said panel and operable on axial movement of the shaft to actuate said switch.

KENNETH A. HARMON. 

